The position precision and dynamic stability of optical elements for an off-axis Three-mirror Anastigmatic (TMA) space remote sensor are dependent on its main support structure, therefore, this paper researches the design scheme of the main support structure for the TMA space remote sensor. After analysis of the common forms of main support structure, a composing of truss support structure was determined, and its materials and connection technique were discussed. The analytical solution for the first order natural frequency of the structure with three struts was derived and the best one was selected. On the basis of a original design, the sensitivity analysis and parameter optimization were used to obtain a main support structure with 24 struts, then it was verified by the static reversal and a dynamic test. Test results show that the front rotation angle change of the main support structure is less than 10″and the first order natural frequency is 55 Hz, when it flips from a vertical state to a horizontal state. Furthermore, the maximum stress of the main support structure is 135 MPa during dynamic tests, which meets the design requirements of all indexes.